early Mac (Mc5) parts

[ted johnson]

Dave, I would bet that the Mc6 and stroker Mc10 piston used the exact same casting number, but a different machining, thus a different part No. I don't think mac decided to bring out the stroker until the Mc6's began outrunning the '10's! I don't see a different piston on the stock stroke Mc10 than the 55310A. The stroker piston is 48832, and the '6 piston is 48844. The Mc20 piston is different yet from the Mc6 and the stroked '10. I still do not see any evidence that Mac released a 1.5" stroke Mc10 with a thin-ring piston.
I screwed up one of the engine mount side plate studs on my 101/Mc20 clone. Broke it off, and it won't "easy-out" out! Later. TJ

[david a luciani]

Ted,

i thought that the later mc10's had thin ring pistons.
is this incorrect?
second the casting could indeed be the same with a different machining operation.
all pistons are cast without the ring lands and those are added later.
also the pin holes aren't bored which i'd be curious to know if the repops Terry Ives has made could have a different pin position drilled to allow use in the older motors.

i haven't checked the mc10 pistons yet but most of the mcculloch pistons have a tiny ledge inside the piston at the top to allow for the ring land machining.
it's only big enough to allow the rings to be placed in one area.
the reason i looked was i thought about cutting a new ring land in a lower position and leaving the upper ring slot open.
not the best practice but it would allow newer mc pistons to be used in older engines without finding a quick time piston.
anyway so far that's not possible with the pistons i've seen.

maybe you'd be able to help me with another motor i have.
it's a mc10 that i bought from the original owner that has a thin ring piston in it. (140$ and i was so new i thought maybe i'd spent too much)
he said it was a gopower mc10 and it does have a gopower manifold and stuffer on it.
it even has blue paint on the piston that the fellow oversprayed when he tried a repaint back in the day.
it might be stroked but the head gasket doesn't look like a .125 to me.
i've never done anything with that motor since it's really solid and has not been ported or modified.
it will get a stock restore job done eventually.
my question is did gopower sell reworked mc10's and what was done to them if they did.
thanx dave

[Tom Smith]

Hey all, the Mc-10 Power Kit Piston Assembly which is P/N 48833 by the way, is .0625" taller above the top ring groove, the ring grooves aren't moved. They are thin. Figure this out before you confuse yourselves more if you don't know what you're talking about.
Mc-10 Power Kit Piston P/N 48833 (std. bore) Mcculloch specs. Oversize are the same plus oversize.
above top ring - 2.1165/2.1170
below top ring - 2.1190/2.1195
bottom skirt - 2.1195/2.1200
The Mc-5/6 head gasket was increased to .080" in production line engines using P/N 48816 head gasket to reduce combustion chamber temperature.
Dave, A stroked Mc-10 requires an aluminum shim between the stuffer and crankcase which besides the 1/8" head gasket is the other visual cue for a power kit equipped Mc-10.
Go Power reworked West Bends and published a booklet about it, I don't know about McCullochs but if the ports are not modified it sounds more like an Mc-10 with merely the additional Go Power parts installed. Some of the things they would have done was add their full circle kit to the crankshaft, modify the ports, and stuff the piston.
Mcculloch used the same powerhead on various different direct drive and gear drive saws. Depending on which drive style it was they stamped out the other model. Example, 1-70 direct drive and 1-80 gear drive saws, since that's what an Mc-10 is, both used the same motor. If it's a 1-80 gear drive then the 1-70 is crossed out and visa-versa, or if both 1-70 and 1-80 are crossed out and it's stamped Mc-10 then it was built up an Mc-10. They were not just switching parts around like David makes it sound, it was to identify if it was used with a direct drive or a gear drive saw. They used 3 codes for the little yellow dudes, DD, GD, and K.

[ted johnson]

Hi, Tom. the 48832 number I quoted is the piston assembly number from the IPL on REAR. There isn't a number listed for the bare piston. Down in the installation notes, there is a ref under "Important", in note "B" to a 48833 as a .010 oversize piston assembly. I wonder if they had put out two IPL's due to a mistake in part numbers? I haven't seen a stroker '10 kit since about '64, so it's hard to remember what they did with it, as far as the grooves and crown height went. I was only pretty sure that the stroker '10 piston was not the same as the Mc6 unit. Thanks for the numbers! Someday I'd like to build another stroked '10. TJ

[Tom Smith]

Ted, yes you're right. I built a stroker 10 for Haddock but used a single ring Wiseco stroker piston. Just wait till you go to put the head shroud on with the thicker head gasket installed! Tom
P/N 48832 STD
P/N 48833 + 0. 010"
P/N 48834 + 0.020"
P/N 48835 + 0.030"

[ted johnson]

Tom: Yep, it sure wants to sit crooked! Dad had a friend with a mill take that built-in spacer on the '10 head down so the shroud sat flat. I can't remember if he milled the fins or not, but I bet he did. Anyhow, I used that same head on all three of my stroker Mac 10's. Dad had switched to an Mc20, then an Mc30 in Super Heavy, and I had tried them too, all equally modified. In fact, I had started with a modified '20, and Dad's stroker Mc10 was faster, though Dad was quite heavy. My stroker Mc10 setup won the Brevard Co., FL Super A championship 1961, '62 and '63. I finally modified an Mc40 that was as fast as the Mc10's, and of course it was a lot stronger physically. The stuffer ears kept breaking on the '10's fragile blocks, and the rods were weak, but boy, were they fast! When I finally sold the '62 Stinger with the Helix gearbox, I kept the '10 and sold the kart with the Mc40 installed. I was a kid of 17 or 18, and I can't remember the part numbers any more. Heck, the numbers I cared about then were "413 long ram", and "35c" cups! Besides, we never used Mac pistons anyhow. We always had Wiseco put the rings where we needed them for our porting. I really appreciate your historic knowledge. It comes in handy! Ted

[david a luciani]

Wow Tom,
excellent information .
as i said mine was speculation and solid numbers are better.
will be saving this post in my info sheets.
thanx all for a great thread.
dave

[Jeff Campbell]

Steve,
FYI - there is another thread from last year that covers the MC5 sidecover and nameplate:

http://rearenginekarts.com/phpBB30/view ... =mc5#p5908

lots of photos and references to cross over chainsaw parts and where to get repro name plates on aluminum backers (the original MC5 plates are not flimsy stickers).

What I found out, was that there was a lot of variation in how McCulloch built those MC5 engines ... they only built them for a very short period until the MC6 came out, but in the short period they used different sidecovers and placed the nameplate in different locations and orientations! So, you get to choose here!

Also, when I built my MC5 look alike motor last year, I used a MC7 piston, a standard 100cc rod, and a MC6 (1.500" stroke) crank, a .065" head gasket, and a Mac coil rebuild kit (has longer plug wire). Once you go to a 1.635" stroke crank that top ring pops out with a MC7-8-9 piston, the stroker pistons with rings set lower are hard to find ... I thought it would be possible to simply leave off the top ring on a MC7-8-9 piston (or regular 91 series piston, if boost porting the block) and go with the standard 1.635" crank ... has anyone tried running a motor like this, any issues with the open top ring groove moving in and out of the top of the cylinder????

I always thought it was funny how the Mac marketing guys talked about moving the spark plug to the other side on the MC6 as if it was some high performance revelation discovered by Mac Research and Development ... when in fact at the time they moved it to the other side on the chainsaws to keep it covered and free from saw wood chips / dust, then conveniently used those same newer saw model parts on the MC6.

I think the MC5 is a really cool motor, very unique in appearance ... I really like running the look-a-like one I built, it fires right up, runs and runs, lots of fun.

Jeff

[ted johnson]

Thanks, Jeff. I ordered the aluminum nameplates a couple days ago from Robbin Loois. He's going to check Saturday to be sure he has some. I also ordered one each for Charlie's Mc6 and Mc7.
My Mc5 will have the saw crank converted to straight 3/4" PTO by Scott Kneisel; the one he did earlier looks great. The flywheel shroud also comes from Scott. Ron Cubel had the block and the crankcase cover (inner shroud). We'll use a '91 rod and a Mc6 or 7 piston, and a '6 head if Ron has one. The bore is about +.020. Exhaust will be squared, but no 9-ports. Intakes are stock. I will use the single Hovey manifold and a later Tilly on alcohol. I have a new 11T Noram clutch coming for it. I'm still looking for an early Palmini header for the little bear. This has been a great thread, and I thank everybody! TJ

[Tom Smith]

Ted, the head shroud has to be in the exact position it was before so the fan housing which captures the left side of the head shroud will still do so. The head fins get pruned too.
Here's Mcculloch's drawing for the thin ring Mc 5, Mc 6, Mc 10, and the Super Mc 10 replacement pistons which were available in Dec. 1960. These had the revised clearance dimensions I listed somewhere.
Those were the only 4 Mcculloch kart motors in existence at that point.

Mc 5 6 10 piston .JPG

(814.63 KiB) Not downloaded yet

stroker Mc-10 block.JPG

(368.68 KiB) Not downloaded yet

Mc-10 stroker .jpg

(122.22 KiB) Not downloaded yet